Bichromophoric methine and azamethine dyes and process for transferring them

ABSTRACT

Bichromophoric methine and azamethine transfer dyes have the formula 
     
         Z.sup.2 --Z.sup.1 --LY.sup.1 --Y.sup.2 
    
     where 
     L is a bridge member which does not permit any conjugation of π-electrons between Z 1  and Y 1 , 
     Y 1  and Z 1  are each independently of the other aminophenylene, which may be benzofused, or heterocyclyl and 
     Y 2  and Z 2  are each independently of the other benzoquinoeiminyl, which may be benzofused, or heterocyclyl.

The present invention relates to novel bichromophoric dyes of the formula I

    Z.sup.2 --Z.sup.1 --L--Y.sup.1 --Y.sup.2                   (I)

where

L is a bridge member which does not permit any conjugation of π-electrons between Z¹ and Y¹,

Z¹ and Y¹ are identical or different and, together with the bridge member L, each is independently of the other a radical of the formula ##STR1## where

n is 0 or 1,

R¹ and R⁵ are identical or different and each is independently of the other alkyl, alkoxyalkyl, alkoycarbonylalkyl or alkanoyloxyalkyl, which may each have up to 10 carbon atoms and be hydroxy- or cyano-substituted, hydrogen, benzyl, cyclohexyl, phenyl or tolyl,

R² and R³ are identical or different and each is independently of the other hydrogen, C₁ -C₈ -alkyl, C₁ -C₆ -alkoxy, C₁ -C₆ -alkanoylamino or C₁ -C₆ -alkylsulfonylamino,

R⁴ is hydrogen, halogen, C₁ -C₈ -alkyl, unsubstituted or C₁ -C₄ -alkyl- or C₁ -C₄ -alkoxy-substituted phenyl, unsubstituted or C₁ -C₄ -alkyl- or C₁ -C₄ -alkoxy-substituted benzyl, cyclohexyl, thienyl or -NHR¹, where R¹ is as defined above, and

R⁵ is hydrogen or C₁ -C₈ -alkyl, and

Z² and Y² are identical or different and each is independently of the other a radical of the formula ##STR2## where

X is nitrogen or CH,

R⁷ is C₁ -C₆ -alkoxycarbonyl, C₁ -C₆ -monoalkylcarbamoyl, C₁ -C₆ -monoalkyl C₁ -C₆ -alkanoylamino or C₁ -C₆ -alkylsulfonylamino, wherein alkyl may in each case be interrupted by 1 or 2 oxygen atoms, or C₅ -C₇ -cycloalkoxycarbonyl, C₅ -C₇ -monocycloalkylcarbamoyl, C₅ -C₇ -monocycloalkylsulfamoyl, C₅ -C₇ -cycloalkylcarbonylamino,phenoxycarbonyl,monophenylcarbamoyl, monophenylsulfamoyl, benzoylamino, phenylsulfonylamino, methylsulfonylamino, fluorine or chlorine,

R⁸ is C₁ -C₈ -alkyl, C₁ -C₆ -alkanoylamino or C₁ -C₆ -alkylsulfonylamino, wherein alkyl may in each case be interrupted by 1 or 2 oxygen atoms, or C₅ -C₇ -cycloalkylcarbonylamino, C₅ -C₇ -cycloalkylsulfonylamino, benzoylamino, phenylsulfonylamino, hydrogen, fluorine or chlorine,

R⁹ is hydrogen or C₁ -C₈ -alkyl which may be interrupted by 1 or 2 oxygen atoms,

R¹⁰ is phenyl or C₁ -C₄ -alkylphenyl,

R¹¹ is C₁ -C₈ -alkyl or C₁ -C₆ -dialkylamino, and

R¹² is hydrogen or C₁ -C₈ -alkyl.

Bichromophoric methine dyes with dicyanovinyl groups are known from GB-A-1 201 925, U.S. Pat. No. 3,553,245, DE-A-1 569 678, DE-A-2 519 592 and DE-A-3 020 473.

It is an object of the present invention to provide novel bichromophoric methine and azamethine dyes which should have advantageous application properties.

We have found that this object is achieved by the bichromophoric dyes of the formula I defined at the beginning.

The bridge member L, which does not permit any conjugation of π-electrons between Z¹ and Y¹, generally conforms to the formula

    --E.sup.1 --D--E.sup.2 --

where

D is a chemical bond, oxygen, --SO₂ --, --O--CO--O--, 1,4-cyclohexylene, phenylene, --O--CO--(CH₂)₁ --CO--O, --O--(CH₂)_(m) --O--, ##STR3## where 1 is from 1 to 10 and m is from 2 to 10, ##STR4## E¹ and E² are identical or different and each is independently of the other a chemical bond or C₁ -C₁₅ -alkylene.

Any alkyl and alkylene appearing in the abovementioned formulae may be either straight-chain or branched.

A suitable R¹, R², R³, R⁴, R⁵, R⁶, R⁸, R¹⁰ and R¹¹ is for example methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, pentyl, isopentyl, neopentyl, tert-pentyl, hexyl, 2-methylpentyl, heptyl, octyl, 2-ethylhexyl or isooctyl.

R¹ and R⁵ may each also be for example nonyl, isononyl, decyl, isodecyl, 2-methoxyethyl, 2-ethoxyethyl, 2-propoxyethyl, 2-butoxyethyl, 2- or 3-methoxypropyl, 2-or 3-ethoxypropyl, 2- or 3-propoxypropyl, 2- or 3-butoxypropyl, 4-methoxybutyl, 4-ethoxybutyl, 4-butoxybutyl, 2-cyanoethyl, 3-cyanopropyl, 4-cyanobutyl, 2-hydroxyethyl, ##STR5##

R⁴ may also be for example phenyl, 2-, 3- or 4-methylphenyl, 2- or 4-isopropylphenyl, 2-butylphenyl, 2-, 3- or 4-methoxyphenyl, 2-propoxyphenyl, 4-butoxyphenyl, 2-(but-2-oxy)phenyl, benzyl, 2-, 3- or 4-methylbenzyl, 2-, 3- or 4-methoxybenzyl, fluorine, chlorine, bromine, 2-thienyl or 3-thienyl.

R² and R³ may each also be methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, sec-butoxy, pentyloxy, isopentyloxy, neopentyloxy or hexyloxy.

R², R³ and R⁸ may each also be for example formylamino, acetylamino, propionylamino, butyrylamino, methylsulfonylamino, ethylsulfonylamino, propylsulfonylamino, isopropylsulfonylamino or butylsulfonylamino.

R⁷ is for example methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, isopropoxycarbonyl, butoxycarbonyl, 2-methoxyethoxycarbonyl, methylcarbamoyl, ethylcarbamoyl, 2-methoxyethylcarbamoyl, cyclopentyloxycarbonyl, cyclohexyloxycarbonyl, cycloheptyloxycarbonyl, cyclopentylcarbamoyl, cyclohexylcarbamoyl, cycloheptylcarbamoyl, methylsulfamoyl,ethylsulfamoyl2-methoxyethylsulfamoyl, cyclopentylsulfamoyl, cyclohexylsulfamoyl, cycloheptylsulfamoyl, methylsulfonylamino, ethylsulfonylamino or p-methylphenylsulfonylamino.

R¹¹ and R⁸ may also be for example cyclopentylcarbonylamino, cyclohexylcarbonylamino or cycloheptylcarbonylamino.

R⁸ may also be for example cyclopentylsulfonylamino, cyclohexylsulfonylamino or cycloheptylsulfonylamino.

R⁹ may also be for example 2-methoxyethyl, 2-ethoxyethyl or 3,6-dioxaheptyl.

R¹⁰ may also be for example 2-, 3- or 4-methylphenyl or 2-, 3- or 4-ethylphenyl.

R¹¹ may also be for example dimethylamino, diethylamino, dipropylamino, diisopropylamino or dibutylamino.

E¹ and E² are each for example methylene, 1,2-ethylene, ethylidene, 1,2- or 1,3-propylene or 1,4-, 1,3- or 2,3-butylene.

D is for example ##STR6##

Preference is given to dyes of the formula I in which Z¹ -L and Y¹ -L conform to the formulae IIa to IIh and Z² and Y² conform to the formula IIIe or IIIf and R¹, R², R³, R⁴, R⁵, R⁶ and R¹² are each as defined above.

Preference is further given to dyes of the formula I in which Z¹ -L and Y¹ -L conform to the formulae IIa to IIj and Z² and Y² conform to the formula IIIa, IIIb or IIIc and R¹, R², R³, R⁵, R⁶, R⁷, R⁸ and R⁹ are each as defined above.

Preference is further given to dyes of the formula I in which Z¹ -L and Y¹ -L conform to the formula IIi, IIj or IIk and Z² and Y² conform to the formula IIId and R¹⁰ and R¹¹ are each as defined above.

Preference is further given to dyes of the formula I in which

R¹ and R⁵ are each independently of the other hydrogen, unsubstituted or cyano- or acetyl-substituted C₁ -C₆ -alkyl or cyclohexyl,

R² and R³ are each independently of the other hydrogen, methyl, methoxy or acetylamino,

R⁴ is hydrogen, C₁ -C₆ -alkyl or unsubstituted or methyl- or methoxy-substituted phenyl, 2-thienyl or 3-thienyl, and

R⁶ is hydrogen or C₁ -C₆ -alkyl.

Preference is further given to dyes of the formula I in which

R⁸ is hydrogen, C₁ -C₆ -alkyl or C₁ -C₆ -alkanoylamino and

R⁹ is hydrogen or C₁ -C₆ -alkyl which may be interrupted by an oxygen atom.

Particular preference is given to dyes of the formula I in which the bridge member L has the formula

    --E.sup.1 --D--E.sup.2 --

where

E¹ and E² are each independently of the other C₁ -C₄ -alkylene and

D is a chemical bond, oxygen, --SO₂ --, --O--CO--(CH₂)₁ --CO--O, ##STR7## where l is from 2 to 4 and m is from 6 to 10, ##STR8##

The dyes I according to the present invention can be obtained in a conventional manner, for example as described in GB 1,201,925, U.S. Pat. No. 3,553,245, DE-A-1,569,678, DE-A-2,519,592, DE-A-3,020,473, U.S. Pat. No. 4,839,336, U.S. Pat. No. 4,541,830, EP-A-147,747, US-A-4,769,360, U.S. Pat. No. 4,695,287, DE-A-3,524,519, U.S. Pat. No. 3,096,339 and U.S. Pat. No. 3,013,013 and in Angew. Chem. 74, (1962), 818.

A preferred procedure comprises for example first linking the later donor groups Z¹ and Y¹ together by means of an appropriate bridge member and then preparing from the resulting intermediates the dyes I by incorporation of the acceptor groups Z² and Y².

By way of illustration see the following synthesis schemes for preparing dyes I (where Z¹, Y¹, R⁷ and R⁸ are in each case as defined above):

a) synthesis of dye intermediates ##STR9##

b) incorporation of acceptors (illustrated with radical IIIa) ##STR10##

Other dye intermediates can be reacted with particular acceptors in the same way.

The novel dyes I are highly soluble in organic solvents.

It is a further object of the present invention to provide a novel process for the thermal transfer of dyes.

In the thermotransfer printing process, a transfer sheet which contains a thermally transferable dye in one or more binders on a support with or without suitable assistants is heated from the back with an energy source, for example a thermal printing head, in short pulses (lasting fractions of a second), causing the dye to migrate out of the transfer sheet and diffuse into the surface coating of a receiving medium. The essential advantage of this process is that the amount of dye to be transferred (and hence the color gradation) is readily controllable through adjustment of the energy to be supplied by the energy source.

In general, color recording is carried out using the three subtractive primaries yellow, magenta and cyan (with or without black). To ensure optimal color recording, the dyes must have the following properties:

ready thermal transferability,

little tendency to migrate within or out of the surface coating of the receiving medium at room temperature,

high thermal and photochemical stability and resistance to moisture and chemical substances,

suitable hues for subtractive color mixing,

a high molar absorption coefficient,

no tendency to crystallize out on storage of the transfer sheet.

From experience these requirements are very difficult to meet at one and the same time.

For this reason, most of the existing thermal transfer printing dyes do not meet the required property profile.

We have found that the further object is achieved advantageously by a process for transferring a bichromophoric methine dye from a transfer to a sheet of plastic-coated paper with the aid of an energy source, which comprises using a transfer on which there is or are one or more dyes of the formula I

    Z.sup.2 --Z.sup.1 --L--Y.sup.1 --Y.sup.2                   (I)

where

L is a bridge member which does not permit any conjugation of π-electrons between Z¹ and Y¹,

Z¹ and Y¹ are identical or different and, together with the bridge member L, each is independently of the other a radical of the formula ##STR11## where

n is 0 or 1,

R¹ and R⁵ are identical or different and each is independently of the other alkyl, alkoxyalkyl, alkoxycarbonylalkyl or alkanoyloxyalkyl, which may each have up to 10 carbon atoms and be hydroxyl- or cyano-substituted, hydrogen, benzyl, cyclohexyl, phenyl or tolyl,

R² and R³ are identical or different and each is independently of the other hydrogen, C₁ -C₈ -alkyl, C₁ -C₆ -alkoxy, C₁ -C₆ -alkanoylamino or C₁ -6-alkylsulfonylamino,

R⁴ is hydrogen, halogen, C₁ -C₈ -alkyl, unsubstituted or C₁ -C₄ -alkyl- or C₁ -C₄ -alkoxy-substituted phenyl, unsubstituted or C₁ -C₄ -alkyl- or C₁ -C₄ -alkoxy-substituted benzyl, cyclohexyl, thienyl or -NHR¹, where R¹ is as defined above, and

R⁶ is hydrogen or C₁ -C₈ -alkyl, and

Z² and Y² are identical or different and each is independently of the other a radical of the formula ##STR12## where

X is nitrogen or CH,

R⁷ is C₁ -C₆ -alkoxycarbonyl, C₁ -C₆ -monoalkylcarbamoyl, C₁ -C₆ -monoalkylsulfamoyl, C₁ -C₆ -alkanoylamino or C₁ -C₆ -alkylsulfonylamino, wherein alkyl may in each case be interrupted by 1 or 2 oxygen atoms, or C₅ -C₇ -cycloalkoxycarbonyl, C₅ -C₇ -monocycloalkylcarbamoyl, C₅ -C₇ -monocycloalkylsulfamoyl, C₅ -C₇ -cycloalkylcarbonylamino, phenoxycarbonyl, monophenylcarbamoyl, monophenylsulfamoyl, benzoylamino, phenylsulfonylamino, methylphenylsulfonylamino, fluorine or chlorine,

R⁸ is C₁ -C₈ -alkyl, C₁ -C₆ -alkanoylamino or C₁ -C₆ -alkylsulfonylamino, wherein alkyl may in each case be interrupted by 1 or 2 oxygen atoms, or C₅ -C₇ -cycloalkylcarbonylamino, C₅ -C₇ -cycloalkylsulfonylamino, benzoylamino, phenylsulfonylamino, hydrogen, fluorine or chlorine,

R⁹ is hydrogen or C₁ -C₈ -alkyl which may be interrupted by 1 or 2 oxygen atoms,

R¹⁰ is phenyl or C₁ -C₄ -alkylphenyl,

R¹¹ is C₁ -C₈ -alkyl or C₁ -C₆ -dialkylamino, and

R¹² is hydrogen or C₁ -C₈ -alkyl.

Compared with the dyes used in existing processes, the dyes transferred in the process according to the invention are notable in general for improved fixation in the receiving medium at room temperature, readier thermal transferability, higher lightfastness, higher stability to moisture and chemical substances, better solubility in organic solvents, higher inked ribbon stability and higher purity of hue.

It is also surprising that the dyes of the formula I are readily transferable and that they have a high inked ribbon stability, despite their very high molecular weight.

Existing thermotransfer printing systems use mixtures of monochromophoric dyes to absorb about one third of the incident white light each in the cyan and in the magenta region. This presents the problem that the dyes used must have exactly the same transfer characteristics to ensure that the same amount of dye is transferred to the acceptor for a given power output of the thermal printing head. The process according to the present invention does not suffer from these disadvantages.

Owing to their high molar extinction coefficients and their high brilliance, the dyes of the formula I employed in the novel process are advantageously suitable for preparing a trichromatic system as required for subtractive color mixing.

In addition, the ready transferability permits wide variation of the receiver or acceptor plastics, and thus makes possible very efficient adaptation of the dyes within the overall system of donor/receiver.

To prepare the dye transfers required in the process according to the present invention, the dyes are incorporated into a suitable organic solvent or solvent mixture together with one or more binders and possibly further assistants to form a printing ink in which the dye is preferably present in a molecularly dispersed, dissolved, form. The printing ink can then be applied to an inert support by knife coating and dried in air.

Suitable organic solvents for the dyes I are for example those in which the solubility of the dyes I at 20° C. is greater than 1% by weight, preferably greater than 5% by weight.

Examples are ethanol, propanol, isobutanol, tetrahydrofuran, methylene chloride, methyl ethyl ketone, cyclopentanone, cyclohexanone, toluene, chlorobenzene and mixtures thereof.

Suitable binders are all resins or polymer materials which are soluble in organic solvents and are capable of binding the dye to the inert support in a form in which it will not rub off. Preference is given to those binders which, after the printing ink has dried in air, hold the dye in a clear, transparent film in which no visible crystallization of the dye occurs.

Examples of such binders are cellulose derivatives, e.g. methylcellulose, ethylcellulose, ethylhydroxyethylcellulose, hydroxypropylcellulose, cellulose acetate and cellulose acetobutyrate, starch, alginates, alkyd resins, vinyl resins, polyvinyl alcohol, polyvinyl acetate, polyvinyl butyrate and polyvinylpyrrolidones. It is also possible to use polymers and copolymers of acrylates or derivatives thereof, such as polyacrylic acid, polymethyl methacrylate or styrene/acrylate copolymers, polyester resins, polyamide resins, polyurethane resins or natural CH resins, such as gum arabic. Other suitable binders are described for example in DE-A-3,524,519.

Preferred binders are ethylcellulose, ethylhydroxyethylcellulose, polyvinyl butyrate and polyvinyl acetate.

The weight ratio of binder:dye is in general within the range from 1:1 to 10:1.

Suitable assistants are for example release agents as mentioned in EP-A-227,092, EP-A-192,435 and the patent applications cited therein. It is also possible to include in particular organic additives which prevent the transfer dyes from crystallizing out in the course of storage or heating of the inked ribbon, for example cholesterol or vanillin.

Inert support materials are for example tissue, blotting or parchment paper and plastics films possessing good heat resistance, for example metallized or unmetallized polyester, polyamide or polyimide. The inert support may additionally be coated on the side facing the thermal printing head with a lubricant or slipping layer in order that adhesion of the thermal printing head to the support material may be prevented. Suitable lubricants are described for example in EP-A-216,483 and EP-A-227,095. The thickness of the support is in general from 3 to 30 μm, preferably from 5 to 10 μm.

The dye-receiving layer can be basically any heat resistant plastics layer having affinity for the dyes to be transferred, for example a modified polycarbonate or polyester. Suitable recipes for the receiving layer composition are described in detail for example in EP-A-227,094, EP-A-133,012, EP-A-133,011, EP-A-111,004, JP-A-199,997/1986, JP-A-283,595/1986, JP-A-237,694/1986 and JP-A-127,392/1986.

Transfer is effected by means of an energy source, for example a laser or a thermal printing head, which must be heatable to ≧300° C. in order that dye transfer may take place within the time range t: 0<t<15 msec. In the course of transfer, the dye migrates out of the transfer sheet and diffuses into the surface coating of the receiving medium.

The dyes according to the present invention are also advantageous for coloring synthetic materials, for example polyesters, polyamides or polycarbonates.

The Examples which follow further illustrate the present invention. Percentages are by weight, unless otherwise stated.

PREPARATION OF DYES Example 1 ##STR13##

3.9 g of bis-2-(N-ethyl-m-toluidino)ethyl sulfone (obtained as described in U.S. Pat. No. 3,553,245) were introduced into 50 ml of glacial acetic acid. 4.2 g of 2,6-dichlorobenzoquinonechloroimine were added at room temperature with vigorous stirring. After the reaction had ended (check by TLC), the reaction mixture was stirred into an ice/water mixture, the resulting mixture was brought to pH 6 with sodium hydroxide solution (10% by weight), and the resulting precipitate was filtered off with suction, washed with water, dried at 40-50° C. under reduced pressure and then chromatographed over silica gel with 5:1 v/v toluene/ethyl acetate.

λ_(max) (CH₂ Cl₂): 634 nm.

R_(f) =0.33 (5:1 v/v toluene/ethyl acetate).

The dyes listed below were obtained by a similar method.

Explanations concerning Table 1:

Dyes of the formula

    Q--W--Q

where W is either ##STR14## The λ_(max) was measured in each case in tetrahydrofuran.

The mobile phase used was

A: ethyl acetate

B: 3:2 v/v toluene/ethyl acetate

C: 8:2 v/v toluene/ethyl acetate

D: 9:1 v/v toluene/ethyl acetate

                                      TABLE 1                                      __________________________________________________________________________     Ex. No.                                                                             Q                W  R.sub.f                                                                           Mobile phase                                                                          λ.sub.max [nm]                       __________________________________________________________________________           ##STR15##       W.sup.1                                                                           0.14                                                                              A      597                                         3                                                                                    ##STR16##       W.sup.2                                                                           0.80                                                                              A      600                                         4                                                                                    ##STR17##       W.sup.2                                                                           0.48                                                                              B      638                                         5                                                                                    ##STR18##       W.sup.2                                                                           0.41                                                                              B      661                                         6                                                                                    ##STR19##       W.sup.1                                                                           0.77                                                                              A      638                                         7                                                                                    ##STR20##       W.sup.2                                                                           0.58                                                                              B      661                                         8                                                                                    ##STR21##       W.sup.1                                                                           0.45                                                                              C      572                                         9                                                                                    ##STR22##       W.sup.2                                                                           0.16                                                                              D      588                                         10                                                                                   ##STR23##       W.sup.1                                                                           0.55                                                                              B      612                                         11                                                                                   ##STR24##       W.sup.2                                                                           0.55                                                                              B      631                                         12                                                                                   ##STR25##       W.sup.2                                                                           0.18                                                                              A      675                                         13                                                                                   ##STR26##       W.sup.2                                                                           0.26                                                                              A      619                                         14                                                                                   ##STR27##       W.sup.2                                                                           0.28                                                                              B      631                                         15                                                                                   ##STR28##       W.sup.2                                                                           0.24                                                                              B      661                                         16                                                                                   ##STR29##       W.sup.2                                                                           0.21                                                                              B      635                                         17                                                                                   ##STR30##       W.sup.2                                                                           0.34                                                                              B      633                                         18                                                                                   ##STR31##       W.sup.2                                                                           0.18                                                                              A      628                                         19                                                                                   ##STR32##       W.sup.1                                                                           0.28                                                                              B      642                                         20                                                                                   ##STR33##       W.sup.1                                                                           0.17                                                                              C      600                                         21                                                                                   ##STR34##       W.sup.1                                                                           0.25                                                                              C      603                                         22                                                                                   ##STR35##       W.sup.1                                                                           0.21                                                                              C      633                                         23                                                                                   ##STR36##       W.sup.2                                                                           0.28                                                                              A      665                                         24                                                                                   ##STR37##       W.sup.1                                                                           0.51                                                                              B      631                                         25                                                                                   ##STR38##       W.sup.2                                                                           0.49                                                                              A      616                                         __________________________________________________________________________

Explanations concerning Table 2

Dyes of the formula

    Q--W--Q

where W is either ##STR39## The λ_(max) was measured in each case in methylene chloride (a) or acetone (b).

The mobile phase used was

A: ethyl acetate

B: 3:2 v/v toluene/ethyl acetate

C: 5:1 v/v toluene/ethyl acetate

                                      TABLE 2                                      __________________________________________________________________________     Ex. No.                                                                             Q                W  R.sub.f                                                                           Mobile phase                                                                          λ.sub.max [nm]                       __________________________________________________________________________     26                                                                                   ##STR40##       W.sup.3                                                                           0.54                                                                              E      633 (b)                                     27                                                                                   ##STR41##       W.sup.3                                                                           0.43                                                                              E      673 (b)                                     28                                                                                   ##STR42##       W.sup.3                                                                           0.45                                                                              E      647 (b)                                     29                                                                                   ##STR43##       W.sup.3                                                                           0.30                                                                              E      673 (b)                                     30                                                                                   ##STR44##       W.sup.3                                                                           0.52                                                                              E      663 (b)                                     31                                                                                   ##STR45##       W.sup.3                                                                           0.58                                                                              E      636 (b)                                     32                                                                                   ##STR46##       W.sup.3                                                                           0,49                                                                              E      675 (b)                                     33                                                                                   ##STR47##       W.sup.4                                                                           0,86                                                                              A      644 (a)                                     34                                                                                   ##STR48##       W.sup.4                                                                           0,69                                                                              A      643 (a)                                     35                                                                                   ##STR49##       W.sup.4                                                                           0,48                                                                              A      614 (a)                                     36                                                                                   ##STR50##       W.sup.4                                                                           0,15                                                                              E      647 (a)                                     37                                                                                   ##STR51##       W.sup.4                                                                           0,18                                                                              A      644 (a)                                     38                                                                                   ##STR52##       W.sup.4                                                                           0,76                                                                              B      612 (a)                                     39                                                                                   ##STR53##       W.sup.4                                                                           0,81                                                                              A      649 (a)                                     40                                                                                   ##STR54##       W.sup.4                                                                           0,89                                                                              A      610 (b)                                     41                                                                                   ##STR55##       W.sup.4                                                                           0,88                                                                              A      615 (b)                                     42                                                                                   ##STR56##       W.sup.4                                                                           0,88                                                                              A      601 (b)                                     43                                                                                   ##STR57##       W.sup.4                                                                           0,74                                                                              B      646 (b)                                     __________________________________________________________________________

EXAMPLE 44 ##STR58## λ_(max) (CH₂ CL₂): 596 nm

R_(f) : 0.25 (ethyl acetate)

EXAMPLE 45 ##STR59##

λ_(max) (CH₂ Cl₂): 670 nm

R_(f) : 0.27 (5:1 v/v toluene/ethyl acetate)

Transfer of dyes

For a simple quantitative examination of the transfer characteristics of the dyes, the thermal transfer was effected with large hotplates instead of a thermal printing head, the transfer temperature being varied within the range 70° C.<T<120° C. while the transfer time was fixed at 2 minutes.

α) General recipe for coating the support with dye: 1 g of binder was dissolved in 8 ml of 8:2 v/v toluene/ethanol at 40-50° C. A solution of 0.25 g of dye in 5 ml of tetrahydrofuran was added with stirring, and any insolubles were filtered off. The print paste thus obtained was applied with an 80 μm doctor blade to a polyester sheet (thickness: 6-10 μm) and dried with a hairdryer.

β) Testing of thermal transferability

The dyes used were tested as follows: The polyester sheet donor containing the dye under test in the coated front was placed face down on commercial receiver paper (specified hereinafter) and pressed down. Donor/receiver were then wrapped in aluminum foil and heated between two hotplates at various temperatures T (within the temperature range 70° C.<T<120° C.). The amount of dye diffusing into the bright plastics layer of the receiver is proportional to the optical density (=absorbance A). The latter was determined photometrically. A plot of the logarithm of the absorbance A of the colored receiver papers measured within the temperature range from 80° to 110° C. against the reciprocal of the corresponding absolute temperature is a straight line from whose slope it is possible to calculate the activation energy ΔE_(T) for the transfer experiment: ##EQU1##

To complete the characterization, it is additionally possible to read from the plots the temperature T* [°C.] at which the absorbance A of the colored receiver papers attains the value 1.

The dyes listed in the tables below were processed according to α), and the dye-coated transfers obtained were tested for their transfer characteristics according to β). The tables show in each case the thermal transfer parameters T* and ΔE_(T), the absorption maxima of the dyes λ_(max) (where measured), the binders used and the weight ratio of dye:binder:assistant.

The key to the abbreviations is as follows:

D=dye

B=binder

EC=ethylcellulose

VL=Vylon® (from Toyobo)

HCVPP=Hitachi Color Video Print Paper (receiver)

VYC=Hitachi VY-C Paper (receiver)

VYT=Hitachi VY-T Paper (receiver)

VYSX=Hitachi VY-SX Paper (receiver)

VYS=Hitachi VY-S Paper (receiver)

SV 100=Kodak Color Video Print Paper (receiver)

    ______________________________________                                         Ex.   Dye    T*      ΔE.sub.T                                            No.   No.    [°C.]                                                                           [kJ/mol]                                                                               B     D:B   Receiver                              ______________________________________                                         46    45     114     86      EC    1:2   SV 100                                47    45     118     70      EC    1:2   HCVPP                                 48     1     150     66      EC    1:2   VYC                                   49     1     120     48      EC    1:2   VYSX                                  50    17      86     42      VL    1:4   VYS                                   51    33     120     32      VL    1:2   HCVPP                                 52    33     114     48      VL    1:2   VYC                                   53    33     101     78      VL    1:2   VYT                                   54    34     107     52      VL    1:2   HCVPP                                 55    34     113     35      VL    1:2   VYC                                   56    34     108     24      VL    1:2   VYT                                   57    35     106     57      VL    1:2   HCVPP                                 58    35     111     51      VL    1:2   VYC                                   59    35     101     75      VL    1:2   VYT                                   60    36     118     61      VL    1:2   VYC                                   61    36     101     82      VL    1:2   VYT                                   62    37      93     78      VL    1:2   VYC                                   63    37      87     69      VL    1:2   VYT                                   64    38     127     47      VL    1:4   HCVPP                                 65    38     122     43      VL    1:4   VYC                                   66    38     107     51      VL    1:4   VYT                                   67    44     138     74      EC    1:2   HCVPP                                 ______________________________________                                    

Explanations concerning Table 4:

Transfer of dyes of the formula

    Q--W--Q

where W is either ##STR60## The λ_(max) was measured in each case in methylene chloride.

                                      TABLE 2                                      __________________________________________________________________________     Ex.                    λ.sub.max                                                                  T* ΔE.sub.T                                    No.                                                                               Q                W  [nm]                                                                              [°C.]                                                                      [kJ/mol]                                                                            B  D:B                                                                               Receiver                               __________________________________________________________________________     68                                                                                 ##STR61##       W.sup.5                                                                           619                                                                               118                                                                               85   EC 1:2                                                                               VYC                                    69                                                                                 ##STR62##       W.sup.5                                                                           627                                                                               129                                                                               88   EC 1:2                                                                               VYC                                    70                                                                                 ##STR63##       W.sup.6                                                                           627                                                                               131                                                                               64   EC 1:2                                                                               HCVPP                                  71                                                                                 ##STR64##       W.sup.6                                                                           596                                                                               138                                                                               74   EC 1:2                                                                               HCVPP                                  71                                                                                 ##STR65##       W.sup.6                                                                           624                                                                               144                                                                               98   EC 1:2                                                                               HCVPP                                  __________________________________________________________________________

The same method can be used to transfer the following dyes:

    __________________________________________________________________________     Ex-                                                                            am-                                                                            ple                                                                            No.                                                                            __________________________________________________________________________     73                                                                                 ##STR66##                                                                  74                                                                                 ##STR67##                                                                  75                                                                                 ##STR68##                                                                  76                                                                                 ##STR69##                                                                  77                                                                                 ##STR70##                                                                  78                                                                                 ##STR71##                                                                  79                                                                                 ##STR72##                                                                  80                                                                                 ##STR73##                                                                  81                                                                                 ##STR74##                                                                  82                                                                                 ##STR75##                                                                  83                                                                                 ##STR76##                                                                  84                                                                                 ##STR77##                                                                  85                                                                                 ##STR78##                                                                  86                                                                                 ##STR79##                                                                  87                                                                                 ##STR80##                                                                  88                                                                                 ##STR81##                                                                  89                                                                                 ##STR82##                                                                  __________________________________________________________________________ 

We claim:
 1. A bichromophoric dye of the formula I

    Z.sup.2 --Z.sup.1 --L--Y.sup.1 --Y.sup.2                   (I)

where L is a bridge member which does not permit any conjugation of π-electrons between Z¹ and Y¹, said bridge member having the formula

    --E.sup.1 --D--E.sup.2 --

where D is a chemical bond, oxygen, --SO₂ --, --O--CO--O--, 1,4-cyclohexylene, phenylene, --O--CO--(CH₂)₁ --CO--O, --O--(CH₂)_(m) --O--, ##STR83## where 1 is from 1 to 10 and m is from 2 to 10, ##STR84## E¹ and E² are identical or different and each is independently of the other a chemical bond or C₁ -C₁₅ -alkylene, Z¹ and Y¹ are identical or different and, together with the bridge member L, each is independently of the other a radical of the formula ##STR85## where R¹ and R⁵ are identical or different and each is independently of the other alkyl, alkoxyalkyl, alkoxycarbonylalkyl or alkanoyloxyalkyl, which may each have up to 10 carbon atoms and be hydroxyl- or cyano- substituted, hydrogen, benzyl, cyclohexyl, phenyl or tolyl, R² and R³ are identical or different and each is independently of the other hydrogen, C₁ -C₈ -alkyl, C₁ -C₆ -alkoxy, C₁ -C₆ -alkanoylamino or C₁ -C₆ -alkylsulfonylamino, Z² and Y² are identical or different and each is independently of the other a radical of the formula ##STR86## where R⁷ is C₁ -C₆ -alkoxycarbonyl, C₁ -C₆ -monoalkylcarbamoyl, C₁ -C₆ -monoalkylsulfamoyl, C₁ -C₆ -alkanoylamino or C₁ -C₆ alkylsulfonylamino, wherein alkyl may in each case be interrupted by 1 or 2 oxygen atoms, or C₅ -C₇ -cycloalkoxycarbonyl, C₅ -C₇ -monocycloalkylcarbamoyl, C₅ -C₇ -monocycloalkylsulfamoyl, C₅ -C₇ -cycloalkylcarbonylamino, phenoxycarbonyl, monophenylcarbamoyl, monophenylsulfamoyl, benzoylamino, phenylsulfonylamino, methylphenylsulfonylamino, fluorine or chlorine, R⁸ is C₁ -C₈ -alkyl, C₁ -C₆ -alkanoylamino or C₁ -C₆ -alkylsulfonylamino, wherein alkyl may in each case be interrupted by 1 or 2 oxygen atoms, or C₅ -C₇ -cycloalkylcarbonylamino, C₅ -C₇ -cycloalkylsulfonylamino, benzoylamino, phenylsulfonylamino, hydrogen, fluorine or chlorine.
 2. The dye of claim 1 or wherein Z¹ and Y¹ are independently selected from the formula IIa.
 3. The dye of claim 1 wherein Z¹ and Y¹ are independently selected from the formula IIe.
 4. The dye of claim 1 wherein Z¹ and Y¹ are independently selected from the formula IIf.
 5. The dye of claim 1 wherein Z² and Y² are independently selected from the formula IIIa.
 6. The dye of claim 1 wherein Z² and Y² are independently selected from the formula IIIb. 